Prototype - How to check several checkboxes

Prototype is a somewhat complex JavaScript library though thoroughly documented it still misses out on some points. For instance, I have a list of checkboxes for which at least one has to be checked. If none of the checkboxes in the group are checked then the user should receive a message indicating the missing action. At first, the most intuitive solution was to use the form.getValues() method in combination with a find() enumerator. However, that method can only loop through an entire form. So I needed a function that could loop through element groups within a form. As always best illustrated with an example:

<ul id="FF_Microsoft">
    <li>
        <input name="FF_MicrosoftDislike" id="FF_MicrosoftDislike" value="1" type="checkbox" />
        <label for="FF_MicrosoftDislike">I generally dislike Microsoft</label>
    </li>
    <li>
        <input id="FF_MicrosoftNone" type="checkbox" value="1" />
        <label for="FF_MicrosoftNone">No, none of the above</label>
    </li>
</ul>

With the following Javascript:

function IsChecked(el) {
    return $$('#' + el + ' input').find(
        function(e) {return e.checked;}); 
};

And in order to use the function you simply:

if(IsChecked('FF_Microsoft') != null)
{
    // Do something
};

The naming used in the example may seem a bit strange (its from my upcoming questionnaire).